The Roman historian Tacitus, writing in Germania, mentioned the Frisians among people he grouped together as the Ingvaeones. Their territory followed the coast of the North Sea from the mouth of the Rhine river up to that of the Ems, their eastern border according to Ptolemy's Geographica. Pliny states in Belgica that they were conquered by the Roman general Drusus in 12 BC, and thereafter the Frisians largely sank into historical obscurity, until coming into contact with the expanding Merovingian and Carolingian empires. In the 5th century, during this period of historical silence, many of them no doubt joined the migration of the Anglo-Saxons who went through Frisian territory to invade Britain, while those who stayed on the continent expanded into the newly-emptied lands previously occupied by the Anglo-Saxons. By the end of the sixth century the Frisians occupied the coast all the way to the mouth of the Weser and spread farther still in the seventh century, southward down to Dorestad and even Bruges. This farthest extent of Frisian territory is known as Frisia Magna.

The modern remnants of Frisia Magna are small and scattered. Most of it got caught in the pincer maneuvers of its expanding neighbors, that of the Saxons who were moving up into their north and west, and the Franks who were pushing into the north and east. Western and Middle Frisia are solidly within modern state of the Netherlands, which now includes the "heartland" of the Frisians from the North Sea coast from Alkmaar in the modern province of Noord-Holland, along the coasts of the modern provinces of Friesland and Groningen, and up to the mouth of the Ems. Culturally, it has shrunk down to the province of Friesland alone. The Frisian language is now spoken only there and in parts of only the Wadden Sea islands of Terschelling and Schiermonnikoog. Eastern and Northern Frisia have been absorbed into the northern states of Germany, with only the marshes of Saterland, well inland from the coast, still retaining any cultural identity. There are also descendants of Frisians living on the coast of the Jutland peninsula and nearby islands. It is unclear when they arrived there, or even whether they lived first on the islands and then spread to the mainland, or vice-versa. What remains of their language is under heavy pressure from Low German, High German, and Danish, and is generally expected to become extinct.

See also: Frisia